Magnetic components, such as inductors and transformers, have posed challenges to the industry due to their structure, which has conventionally included winding wire having a circular cross-section about a bobbin-like core into an often bulky and non-uniform structure which can not be readily handled by vacuum handling devices, as described in U.S. Pat. No. 5,182,536 of Boylan et al.
New operational requirements with respect to circuit size and power density and increasing necessity to reduce circuit manufacturing costs have made the traditional wire-would magnetic component an unattractive element due to its space requirements and the conflicting design criterion of minimizing space requirements of necessary circuit blocks, e.g., power supply circuits. Attaining these conflicting design objectives has required the redesign of magnetic devices to achieve a low profile.
In the recent years, so called "planar magnetics" have been developed and accepted in the industry for high density, high frequency applications, e.g., planar transformers for use in power supplies. Such magnetic devices are generally constituted by a stack of planar copper windings. Planar transformers of such construction have been characterized by desirable electrical and mechanical characteristics such as low weight, high efficiency, and low leakage inductance. The low profile package of such transforms means that the transformer no longer determines the overall height of a power supply.
An example of such a magnetic device is a low-profile planar transformer. Such a transformer typically includes a primary winding formed as a spiral of conductive traces on a planar surface and one or more secondary windings which are formed in the same manner, with the primary and secondary windings being electromagnetically coupled by a core of magnetically permeable material. Such planar transformer designs have enabled control over critical dimensions, and have made the production and assembly of power supply components simple and repeatable; however, the manufacture of planar transformers has been complicated by the need for termination pins to connect the planar coils to external circuitry. In addition, known magnetic devices have not adequately addressed the problem of providing pin-less connections to multiple windings of a single planar magnetic device.
Generally, planar magnetics have used various types of termination pins to physically (e.g., electrically or mechanically) connect the device to an electrical circuit. U.S. Pat. No. 3,833,872 of Marcus et al. is one such example which is hereby incorporated by reference as if set forth in its entirety herein. The '872 patent discloses a monolithic transformer that is formed by laminating a plurality of planar sheets, some of which have conductive spirals and others of which provide insulation. The planar sheets are pre-arranged to result in a laminated transformer of predetermined design with selectively placed conductive vias connecting the stacked layers to one another. The manufacturing method of the '872 patent causes a plurality of transformers to be made simultaneously; the individual transformers being cut from a sintered, laminated structure. Metal terminations are attached to the transformer in a conventional manner as a final step in the process. However, there are several drawbacks associated with the termination of planar devices using pins as in the Marcus et al. process.
For example, the electrical connection between the planar device and a printed circuit board ("PCB") relies on the integrity of an intermediate connection of each to a termination pin, that is, an additional element. The integrity of the electrical connection relies on contact with a plated through hole ("via") of the PCB, and the integrity of the mechanical connection relies upon the mechanical alignment of several vias of the PCB to the termination pins of the magnetic device.
A surface-mount inductive device has been proposed in U.S. Pat. No. 5,363,080 of Breen which is connectable to a PCB without any termination pins. The U.S. Pat. No. 5,363,080 patent is hereby incorporated by reference as if set forth in its entirety herein. The inductor is constructed by successively forming layers upon a single supporting substrate. Purportedly, this method of manufacture provides the designer with highly accurate control over the value of the inductance in the resulting inductor. The method proposed by Breen, however, requires that the inductor be formed in a serial manner, that, is layer by layer, which imposes constraints on the throughput of a manufacturing facility.
The present invention is aimed at overcoming one or more difficulties in the art of manufacturing pin-less, planar magnetic devices.